High-toughness Al-Si series cast aluminum alloy and preparation method thereof

Abstract

The invention discloses a high-toughness Al-Si series cast aluminum alloy and a preparation method thereof. The high-toughness Al-Si series cast aluminum alloy is composed of, by mass, 6.5%-7.5% of Si, 0.12% of Fe, 0.1%-0.3% of Cu, 0.02% of Mn, 0.3%-0.5% of Mg, 0.1%-0.5% of Ti, 1.5%-2.0% of Zn, 0.02%-0.04% of Sr, 0.1%-0.2% of Zr and the balance Al and inevitable impurity elements. In the inevitable impurity elements, the mass percentage of a single impurity element is smaller than or equal to 0.05%, and the total mass percentage of the impurity elements is smaller than or equal to 0.15%; according to the invention, based on the Al-Si alloy, the contents of Cu, Mg and Zn are designed and increased, and the strength and plasticity of the Al-Si alloy are synergistically improved by utilizing a synergistic strengthening mechanism of complex multi-phase Mg2Si phase, S (Al2CuMg) phase and T (Al2Mg3Zn3) phase of the Cu, the Mg and the Zn and adding Sr and Zr at the same time.

Description

Technical Field

[0001] This invention relates to the field of alloy technology, and in particular to a high-strength and high-toughness Al-Si cast aluminum alloy and its preparation method. Background Technology

[0002] Al-Si cast aluminum alloys, with their excellent casting fluidity, low susceptibility to hot cracking, good corrosion resistance, and superior specific strength, have become indispensable key materials in modern industry. From complex thin-walled automotive engine blocks, gearbox housings, and electric motor end caps in new energy vehicles, to lightweight and reliable aerospace brackets, precision instrument frames, and hydraulic valve bodies, and to various industrial pump housings and power tool housings, their presence is ubiquitous, forming the "lightweight skeleton" of transportation, high-end equipment, and energy power. Statistics show that cast aluminum alloys account for over 70% of lightweight automotive materials, with Al-Si alloys holding an absolute dominant position, and their application breadth and depth continue to expand.

[0003] However, with the continuous increase in the performance requirements of end products, especially the pursuit of high efficiency and high power density of electric drive systems in new energy vehicles, the extreme requirements of weight reduction and safety margin in aerospace equipment, and the development of engineering machinery towards high power and long life, the mechanical performance bottleneck of traditional Al-Si casting alloys (such as widely used but limited in comprehensive performance grades A356 / A360 and A319) is becoming increasingly prominent.

[0004] The core contradiction lies in the difficulty of synergistically improving strength and toughness at a high level. Strength limitations: the room temperature tensile strength of traditional alloys is typically 250-320 MPa (e.g., A356-T6). Higher strength requirements (e.g., above 350 MPa) often rely on excessive addition of strengthening elements such as Cu and Mg, which significantly impairs casting performance and corrosion resistance, and increases the risk of hot cracking. Insufficient toughness: the natural brittleness of the eutectic silicon phase, especially when not fully modified, manifests as coarse needle-like structures, becoming stress concentration sources and crack initiation points. Furthermore, unavoidable Fe impurities easily form the hard and brittle β-Al5FeSi phase (especially when the cooling rate is insufficient, manifesting as coarse needles), further fracturing the matrix. This results in the elongation of typical high-silicon alloys (e.g., A413) generally being less than 3%, severely restricting the service safety and lifespan of components under complex alternating loads (e.g., engine vibration, chassis impact). For example, the housing of high-speed motors in new energy vehicles faces the dual challenges of high cyclic mechanical stress and thermal stress under extreme working conditions. Traditional materials are prone to fatigue cracks in stress concentration areas. Shortcomings in thermal strength: at high temperatures (>150°C), traditional alloys that are mainly strengthened by metastable precipitates (such as Mg2Si, Al2Cu) are prone to coarsening and dissolution of their strengthening phases, resulting in a sharp decline in strength, hardness and creep resistance, which makes it difficult to meet the usage requirements of high-temperature components (such as turbocharger housings and cylinder head hot zones).

[0005] Current strengthening and toughening modifications of Al-Si alloys mainly focus on alloy composition optimization, melt purification, efficient modification refinement, and heat treatment process control. For example, Sr or Sb modification refines the eutectic silicon morphology; adding elements such as Mn and Cr neutralizes the harmful effects of Fe, promoting Fe phase spheroidization or transformation into a less harmful morphology (such as α-Al15(Fe, Mn)3Si2); optimizing the content and ratio of Mg and Cu; and applying T6 and T7 solution aging heat treatments to fully explore the precipitation strengthening potential.

[0006] However, the aforementioned conventional technical routes are gradually approaching their performance limits, mainly in the following aspects: Unstable modification effects: Sr is easily burned off, the Sb effect is greatly affected by the cooling rate, and excessive modification may introduce new casting defects; Difficulty in controlling the Fe phase: Completely eliminating Fe is neither economical nor realistic; while adding Mn / Cr can improve the Fe phase morphology, excessive addition will form new large-sized primary phases, damaging toughness and casting performance, and its inhibitory effect on extremely fine Fe phases is limited; The challenge of balancing strength and toughness: Increasing the content of strengthening elements to improve strength often comes at the cost of sacrificing elongation and impact toughness, and vice versa. Narrow heat treatment process window, failing to fully release the strengthening and toughening potential; Thermal stability bottleneck: The inherent thermal instability of existing precipitated strengthening phases is difficult to completely solve through conventional composition and heat treatment.

[0007] Therefore, developing a novel high-strength and high-toughness Al-Si cast aluminum alloy that overcomes existing technological limitations and achieves high strength (e.g., tensile strength ≥335MPa), high toughness (elongation ≥8%), excellent thermal stability, and good casting processability, along with its efficient, stable, and controllable preparation method, has become a focus of common attention in academia and industry. This is not only a necessary requirement to meet the extreme service performance requirements of key castings for the next generation of high-end equipment, but also a core material guarantee for promoting the in-depth development of lightweight technology and achieving the national strategic goals of energy conservation and emission reduction. Summary of the Invention

[0008] The purpose of this invention is to provide a high-strength and high-toughness Al-Si cast aluminum alloy and its preparation method, so as to solve the problems existing in the prior art.

[0009] A high-strength and high-toughness Al-Si cast aluminum alloy is composed of the following components by mass percentage: Si: 6.5-7.5%, Fe: 0.12%, Cu: 0.1-0.3%, Mn: 0.02%, Mg: 0.3-0.5%, Ti: 0.1-0.5%, Zn: 1.5-2.0%, Sr: 0.02-0.04%, Zr: 0.1-0.2%, with the balance being Al and unavoidable impurity elements; among the unavoidable impurity elements, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of impurity elements is ≤0.15%.

[0010] Preferably, the mass percentage ratio of Mg to Zn is ≥0.15, and the mass percentage ratio of Mg to (Cu+Zn) is 0.13-0.31%.

[0011] Preferably, Sr is added in the form of an Al-Sr10 master alloy, and the mass percentage of Sr in the Al-Sr10 master alloy is 10%.

[0012] Preferably, Zr is added in the form of an Al-Zr5 master alloy, and the mass percentage of Zr in the Al-Zr5 master alloy is 5%; Zr forms an Al3Zr dispersed phase with the Al matrix, which is used to refine the primary α-Al phase and pin dislocation movement.

[0013] Preferably, Ti is added in the form of AlTi5B master alloy, and the mass percentage of Ti in AlTi5B master alloy is 5% and the mass percentage of B is 1%.

[0014] A method for preparing a high-strength and high-toughness Al-Si cast aluminum alloy includes the following steps: S1: Raw material preparation: Weigh out A356.2 aluminum ingot, Al-Cu50 master alloy, Al-Zn30 master alloy, magnesium ingot, AlTi5B master alloy, Al-Sr10 master alloy, Al-Zr5 master alloy and refining agent according to the above alloy composition. S2: Melting treatment: The melting furnace is first heated to 520-540℃ and held for 20 minutes, then heated to 750-770℃. A356.2 aluminum ingot, Al-Cu50 master alloy, and Al-Zn30 master alloy are added. After they are completely melted, the temperature is lowered to 740℃ and magnesium ingot is added until they are completely melted. S3: Refining and modification treatment: At 740℃, AlTi5B master alloy is first added to the melting furnace and melted, then Al-Sr10 master alloy and Al-Zr5 master alloy are added until completely melted; S4: Refining process: A protective gas is introduced into the melt, and powdered refining agent is sprayed into the melt and stirred to remove gas and slag. After standing, the composition is analyzed. The refining temperature is 720-740℃, the refining time is 10-20min, the degassing temperature is 725-740℃, and the degassing time is 900-1500s. S5: Low-pressure casting: After the composition test is qualified, the holding furnace is moved to the low-pressure casting equipment; the holding temperature for low-pressure casting is 705-725℃. S6: Heat treatment: The product after low-pressure casting is subjected to solution treatment, water quenching treatment and aging treatment in sequence to obtain a high-strength and tough cast aluminum alloy.

[0015] Preferably, the refining agent in S4 is a chloride or a fluoride or a mixture of chloride and fluoride; the protective gas is at least one of nitrogen, argon and helium.

[0016] Preferably, the forming pressure of the low-pressure casting in S5 is 200-450 mbar, the forming speed is 40-70 mm / s, and the holding time is 65-150 s; the rotor speed of the low-pressure casting equipment is 410-450 r / min.

[0017] Preferably, in S6, the solution treatment temperature is 500-550℃ and the treatment time is 5-6h; the water temperature for water quenching is 50-80℃ and the transfer time from taking it out of the solution furnace to entering the water is <10s; the aging treatment temperature is 100-150℃ and the treatment time is 7-8h, followed by air cooling.

[0018] Compared with the prior art, the present invention provides a high-strength and high-toughness Al-Si cast aluminum alloy and its preparation method, which has the following beneficial effects: This invention is based on Al-Si alloys. It designs to increase the content of Cu, Mg and Zn, and utilizes the complex multi-phase structure of the three, the synergistic strengthening mechanism of the Mg2Si phase with the S(Al2CuMg) phase and the T(Al2Mg3Zn3) phase, while increasing Sr and Zr, to achieve a synergistic improvement in the strength and plasticity of Al-Si alloys. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a high-strength and high-toughness Al-Si cast aluminum alloy, composed of the following components by mass percentage: Si: 6.5-7.5%, Fe: 0.08-0.12%, Cu: 0.1-0.3%, Mn: 0.02%, Mg: 0.3-0.5%, Ti: 0.1-0.5%, Zn: 1.5-2.0%, Sr: 0.02-0.04%, Zr: 0.1-0.2%, with the balance being Al and unavoidable impurity elements; among the unavoidable impurity elements, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of impurity elements is ≤0.15%; wherein, the mass percentage ratio of Mg to Zn is ≥0.15, and the mass percentage ratio of Mg to (Cu+Zn) is 0.13-0.31%; Sr is added in the form of Al-Sr10 master alloy, and the mass percentage of Sr in Al-Sr10 master alloy is 10%; Zr is added in the form of Al-Zr5 master alloy, and the mass percentage of Zr in Al-Zr5 master alloy is 5%; Zr forms Al3Zr dispersed phase with Al matrix, which is used to refine primary α-Al phase and pin dislocation movement; Ti is added in the form of AlTi5B master alloy, and the mass percentage of Ti in AlTi5B master alloy is 5% and the mass percentage of B is 1%.

[0021] The above-mentioned high-strength and high-toughness Al-Si cast aluminum alloy is prepared by the following method, including the following steps: S1: Raw material preparation: Weigh out A356.2 aluminum ingot, Al-Cu50 master alloy, Al-Zn30 master alloy, magnesium ingot, AlTi5B master alloy, Al-Sr10 master alloy, Al-Zr5 master alloy and refining agent according to the above alloy composition. S2: Melting treatment: The melting furnace is first heated to 520-540℃ and held for 20 minutes, then heated to 750-770℃. A356.2 aluminum ingot, Al-Cu50 master alloy, and Al-Zn30 master alloy are added. After they are completely melted, the temperature is lowered to 740℃ and magnesium ingot is added until they are completely melted. S3: Refining and modification treatment: At 740℃, AlTi5B master alloy is first added to the melting furnace and melted, then Al-Sr10 master alloy and Al-Zr5 master alloy are added until completely melted; S4: Refining process: A protective gas is introduced into the melt, and a powdered refining agent is sprayed into the melt and stirred to remove gas and slag. After settling, the composition is analyzed. The refining temperature is 720-740℃, the refining time is 10-20 min, the degassing temperature is 725-740℃, and the degassing time is 900-1500 s. The refining agent is a chloride or fluoride or a mixture of chloride and fluoride. The protective gas is at least one of nitrogen, argon, and helium. S5: Low-pressure casting: After the composition test is qualified, the holding furnace is moved to the low-pressure casting equipment; the holding temperature for low-pressure casting is 705-725℃; the forming pressure for low-pressure casting is 200-450mbar, the forming speed is 40-70mm / s, and the holding time is 65-150s; the rotor speed of the low-pressure casting equipment is 410-450r / min. S6: Heat treatment: The low-pressure casting product is subjected to solution treatment, water quenching treatment and aging treatment in sequence to obtain a high-strength and tough cast aluminum alloy; the solution treatment temperature is 500-550℃ and the treatment time is 5-6h; the water quenching temperature is 50-80℃ and the transfer time from taking it out of the solution furnace to entering the water is <10s; the aging treatment temperature is 100-150℃ and the treatment time is 7-8h, followed by air cooling. Example

[0022] A high-strength and high-toughness Al-Si cast aluminum alloy is composed of the following components by mass percentage: Si: 7%, Fe: 0.08%, Cu: 0.1%, Mn: 0.02%, Mg: 0.35%, Ti: 0.1%, Zn: 1.5%, Sr: 0.02%, Zr: 0.1%, with the balance being Al and unavoidable impurity elements; among the unavoidable impurity elements, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of all impurity elements is ≤0.15%.

[0023] The mass percentage ratio of Mg to Zn is ≥0.15 to avoid brittleness caused by the continuity of the T phase at grain boundaries; the mass percentage ratio of Mg to (Cu+Zn) is 0.13-0.31% to avoid the formation of brittle phases due to element segregation; Sr is added in the form of Al-Sr10 master alloy, and the mass percentage of Sr in the Al-Sr10 master alloy is 10%, which can significantly refine the morphology of the eutectic silicon structure, thereby improving the plasticity of the alloy.

[0024] Zr is added in the form of Al-Zr5 master alloy, and the mass percentage of Zr in Al-Zr5 master alloy is 5%; Zr forms Al3Zr dispersed phase with Al matrix, which is used to refine primary α-Al phase and pin dislocation movement, effectively improving the high temperature strength and creep resistance of alloy.

[0025] Ti is added in the form of AlTi5B master alloy, and the mass percentage of Ti in AlTi5B master alloy is 5% and the mass percentage of B is 1%.

[0026] This embodiment describes a method for preparing a high-strength and high-toughness Al-Si cast aluminum alloy, comprising the following steps: S1: Raw material preparation: Weigh out A356.2 aluminum ingot, Al-Cu50 master alloy, Al-Zn30 master alloy, magnesium ingot, AlTi5B master alloy, Al-Sr10 master alloy, Al-Zr5 master alloy and refining agent according to the above alloy composition. S2: Melting treatment: The melting furnace is first heated to 520-540℃ and held for 20 minutes, then heated to 750-770℃. Then, A356.2 aluminum ingot, Al-Cu50 master alloy and Al-Zn30 master alloy are added. After they are completely melted, the temperature is lowered to 740℃, and then magnesium ingot is added until it is completely melted. S3: Refining and modification treatment: At 740℃, AlTi5B master alloy is first added to the melting furnace and melted, then Al-Sr10 master alloy and Al-Zr5 master alloy are added until completely melted; S4: Refining treatment: High-purity nitrogen gas is introduced into the melt, and the powdered refining agent chloride is sprayed into the melt and stirred for 30 minutes to remove gas and slag. After standing for 35 minutes and cooling to 705℃, the composition is analyzed. The amount of refining agent is 0.2wt% of the melt, the nitrogen pressure is 0.03MPa, and the melt temperature is 730℃ during spraying and stirring. S5: Low-pressure casting: After the composition test is qualified, the holding furnace is moved to the low-pressure casting equipment; the forming pressure of low-pressure casting is 400mbar, the forming speed is 66mm / s, the holding time is 120s, and the holding temperature is 715℃. S6: Heat treatment: The low-pressure cast product is solution treated in a continuous flow heat treatment furnace at a solution temperature of 535℃ for 6 hours; then it is quenched by rapid cooling in water at 70℃ with a transfer time of <10s; the aging treatment temperature is 135℃ for 8 hours to avoid T phase coarsening; after aging, it is air-cooled to obtain a high-strength and high-toughness cast aluminum alloy. Example

[0027] A high-strength and high-toughness Al-Si cast aluminum alloy is composed of the following components by mass percentage: Si: 6.8%, Fe: 0.1%, Cu: 0.15%, Mn: 0.02%, Mg: 0.4%, Ti: 0.3%, Zn: 1.7%, Sr: 0.03%, Zr: 0.18%, with the balance being Al and unavoidable impurity elements; among the unavoidable impurity elements, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of all impurity elements is ≤0.15%.

[0028] The mass percentage ratio of Mg to Zn is ≥0.15 to avoid brittleness caused by the continuity of the T phase at grain boundaries; the mass percentage ratio of Mg to (Cu+Zn) is 0.13-0.31% to avoid the formation of brittle phases due to element segregation; Sr is added in the form of Al-Sr10 master alloy, and the mass percentage of Sr in the Al-Sr10 master alloy is 10%, which can significantly refine the morphology of the eutectic silicon structure, thereby improving the plasticity of the alloy.

[0029] Zr is added in the form of Al-Zr5 master alloy, and the mass percentage of Zr in Al-Zr5 master alloy is 5%; Zr forms Al3Zr dispersed phase with Al matrix, which is used to refine primary α-Al phase and pin dislocation movement, effectively improving the high temperature strength and creep resistance of alloy.

[0030] Ti is added in the form of AlTi5B master alloy, and the mass percentage of Ti in AlTi5B master alloy is 5% and the mass percentage of B is 1%.

[0031] This embodiment describes a method for preparing a high-strength and high-toughness Al-Si cast aluminum alloy, comprising the following steps: S1: Raw material preparation: Weigh out A356.2 aluminum ingot, Al-Cu50 master alloy, Al-Zn30 master alloy, magnesium ingot, AlTi5B master alloy, Al-Sr10 master alloy, Al-Zr5 master alloy and refining agent according to the above alloy composition. S2: Melting treatment: The melting furnace is first heated to 520-540℃ and held for 20 minutes, then heated to 750-770℃. Then, A356.2 aluminum ingot, Al-Cu50 master alloy and Al-Zn30 master alloy are added. After they are completely melted, the temperature is lowered to 740℃, and then magnesium ingot is added until it is completely melted. S3: Refining and modification treatment: At 740℃, AlTi5B master alloy is first added to the melting furnace and melted, then Al-Sr10 master alloy and Al-Zr5 master alloy are added until completely melted; S4: Refining treatment: High-purity nitrogen gas is introduced into the melt, and the powdered refining agent chloride is sprayed into the melt and stirred for 30 minutes to remove gas and slag. After standing for 35 minutes and cooling to 705℃, the composition is analyzed. The amount of refining agent is 0.2wt% of the melt, the nitrogen pressure is 0.03MPa, and the melt temperature is 740℃ during spraying and stirring. S5: Low-pressure casting: After the composition test is qualified, the holding furnace is moved to the low-pressure casting equipment; the forming pressure of low-pressure casting is 450mbar, the forming speed is 50mm / s, the holding time is 80s, and the holding temperature is 720℃. S6: Heat treatment: The product after low-pressure casting is solution treated in a continuous flow heat treatment furnace at a temperature of 500℃ for 5 hours; then it is quenched by rapid cooling in water at 75℃ with a transfer time of <10s; the aging treatment temperature is 110℃ for 7 hours to avoid T phase coarsening; after aging, it is air-cooled to obtain a high-strength and high-toughness cast aluminum alloy. Example

[0032] A high-strength and high-toughness Al-Si cast aluminum alloy is composed of the following components by mass percentage: Si: 7.5%, Fe: 0.08%, Cu: 0.3%, Mn: 0.02%, Mg: 0.48%, Ti: 0.5%, Zn: 2.0%, Sr: 0.04%, Zr: 0.2%, with the balance being Al and unavoidable impurity elements; among the unavoidable impurity elements, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of all impurity elements is ≤0.15%.

[0033] The mass percentage ratio of Mg to Zn is ≥0.15 to avoid brittleness caused by the continuity of the T phase at grain boundaries; the mass percentage ratio of Mg to (Cu+Zn) is 0.13-0.31% to avoid the formation of brittle phases due to element segregation; Sr is added in the form of Al-Sr10 master alloy, and the mass percentage of Sr in the Al-Sr10 master alloy is 10%, which can significantly refine the morphology of the eutectic silicon structure, thereby improving the plasticity of the alloy.

[0034] Zr is added in the form of Al-Zr5 master alloy, and the mass percentage of Zr in Al-Zr5 master alloy is 5%; Zr forms Al3Zr dispersed phase with Al matrix, which is used to refine primary α-Al phase and pin dislocation movement, effectively improving the high temperature strength and creep resistance of alloy.

[0035] Ti is added in the form of AlTi5B master alloy, and the mass percentage of Ti in AlTi5B master alloy is 5% and the mass percentage of B is 1%.

[0036] This embodiment describes a method for preparing a high-strength and high-toughness Al-Si cast aluminum alloy, comprising the following steps: S1: Raw material preparation: Weigh out A356.2 aluminum ingot, Al-Cu50 master alloy, Al-Zn30 master alloy, magnesium ingot, AlTi5B master alloy, Al-Sr10 master alloy, Al-Zr5 master alloy and refining agent according to the above alloy composition. S2: Melting treatment: The melting furnace is first heated to 520-540℃ and held for 20 minutes, then heated to 750-770℃. Then, A356.2 aluminum ingot, Al-Cu50 master alloy and Al-Zn30 master alloy are added. After they are completely melted, the temperature is lowered to 740℃, and then magnesium ingot is added until it is completely melted. S3: Refining and modification treatment: At 740℃, AlTi5B master alloy is first added to the melting furnace and melted, then Al-Sr10 master alloy and Al-Zr5 master alloy are added until completely melted; S4: Refining treatment: High-purity nitrogen gas is introduced into the melt, and the powdered refining agent chloride is sprayed into the melt and stirred for 30 minutes to remove gas and slag. After standing for 35 minutes and cooling to 705℃, the composition is analyzed. The amount of refining agent is 0.2wt% of the melt, the nitrogen pressure is 0.03MPa, and the melt temperature is 725℃ during spraying and stirring. S5: Low-pressure casting: After the composition test is qualified, the holding furnace is moved to the low-pressure casting equipment; the forming pressure of low-pressure casting is 300mbar, the forming speed is 70mm / s, the holding time is 145s, and the holding temperature is 710℃. S6: Heat treatment: The low-pressure cast product is solution treated in a continuous flow heat treatment furnace at a solution temperature of 540℃ for 6 hours; then it is quenched by rapid cooling in water at 60℃ with a transfer time of <10s; the aging treatment temperature is 145℃ for 7 hours to avoid T phase coarsening; after aging, it is air-cooled to obtain a high-strength and high-toughness cast aluminum alloy.

[0037] Comparative Example 1: The high-strength and high-toughness cast aluminum alloy prepared in this comparative example has the following chemical composition by mass percentage: Si: 7.2%, Mg: 0.45%, Cu: 0.22%, Zn: 4.0%, Fe: 0.1%, Mn: 0.02%, Ti: 0.35%, Sr: 0.03%, Zr: 0.18%, with the remainder being Al and unavoidable impurity elements.

[0038] The preparation method is the same as in Example 1.

[0039] Comparative Example 2: The high-strength and high-toughness cast aluminum alloy prepared in this comparative example has the following chemical composition by mass percentage: Si: 7.3%, Mg: 0.46%, Cu: 2.76%, Zn: 1.84%, Fe: 0.1%, Mn: 0.02%, Ti: 0.33%, Sr: 0.03%, Zr: 0.1%, with the remainder being Al and unavoidable impurity elements. This comparative example does not contain an aluminum-copper master alloy compared to Example 1.

[0040] The preparation method is the same as in Example 2.

[0041] Comparative Example 3: The high-strength and high-toughness cast aluminum alloy prepared in this comparative example has the following chemical composition by mass percentage: Si: 7%, Mg: 0.4%, Cu: 0.24%, Zn: 0.05%, Fe: 0.1%, Mn: 0.02%, Ti: 0.35%, Sr: 0.03%, Zr: 0.15%, with the remainder being Al and unavoidable impurity elements. This comparative example does not contain an aluminum-zinc master alloy, unlike Example 1.

[0042] The preparation method is the same as in Example 3.

[0043] Comparative Example 4: This comparative example is a cast aluminum alloy without added Sr and Zr, whose chemical composition by mass percentage is: Si: 7%, Mg: 0.38%, Cu: 0.19%, Zn: 1.62%, Fe: 0.1%, Mn: 0.02%, Ti: 0.1%, with the remainder being Al and unavoidable impurity elements.

[0044] The preparation method is the same as in Example 1.

[0045] Table 1. Alloy composition table for examples and comparative examples.

[0046] Table 2 Mechanical properties of alloys from examples and comparative examples

[0047] Tables 1 and 2 show the alloy composition and mechanical properties of the examples and comparative examples, respectively. Analysis of Tables 1 and 2, and a comparison of Examples 1-3 and Comparative Examples 1-4, reveals that by adjusting the ratio of Mg, Zn, and Cu elements and adding trace amounts of Sr and Zr, the present invention achieves the following conclusions: The cast Al-Si alloys obtained by the methods described in Examples 1-3 exhibit significantly higher tensile strength, yield strength, and elongation than aluminum alloys without Sr and Zr. By controlling the ratio of Mg, Zn, and Cu, and by adding Sr and Zr, the distribution of various strengthening and dispersed phases in the matrix was effectively controlled, alleviating the strengthening phase segregation effect. This effectively hindered crack propagation during service, thereby improving the strength and elongation of the Al-Si alloys. When the ratio of Mg, Zn, and Cu exceeds the predetermined range, the elongation of the alloy decreases significantly. Compared with the Al-Si alloys without Sr and Zr, the average tensile strength increased by 18.86%, the average yield strength increased by 21.48%, and the average elongation increased by 83.3%.

[0048] This invention is based on Al-Si alloys. By optimizing the content ratio of Mg, Cu, and Zn alloying elements, while adding Sr and Zr elements, and strictly controlling the content of Fe, Mn, and other elements, the microstructure of the alloy is regulated to improve mechanical properties and casting fluidity, thereby obtaining a high-strength and high-toughness cast aluminum alloy with both high strength and plasticity. The addition of Zn element changes the strengthening mechanism, and Cu, Mg, and Zn form a complex multi-phase structure. Utilizing the synergistic strengthening mechanism of the Mg2Si phase with the S(Al2CuMg) and T(Al2Mg3Zn3) phases, the changes in the solid solution temperature window after Zn addition and the potential hot cracking tendency caused by higher Cu content are considered. At the same time, using Zn instead of expensive Sc as a strengthening path can better focus on the feasibility of industrial production.

[0049] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A high-strength and high-toughness Al-Si cast aluminum alloy, characterized in that, It is composed of the following components by mass percentage: Si: 6.5-7.5%, Fe: 0.08-0.12%, Cu: 0.1-0.3%, Mn: 0.02%, Mg: 0.3-0.5%, Ti: 0.1-0.5%, Zn: 1.5-2.0%, Sr: 0.02-0.04%, Zr: 0.1-0.2%, with the balance being Al and unavoidable impurity elements; among the unavoidable impurity elements, the mass percentage of a single impurity element is ≤0.05%, and the total mass percentage of impurity elements is ≤0.15%.

2. The high-strength and high-toughness Al-Si cast aluminum alloy according to claim 1, characterized in that, The mass percentage ratio of Mg to Zn is ≥0.15, and the mass percentage ratio of Mg to (Cu+Zn) is 0.13-0.31%.

3. The high-strength and high-toughness Al-Si cast aluminum alloy according to claim 1, characterized in that, Sr is added in the form of an Al-Sr10 master alloy, and the mass percentage of Sr in the Al-Sr10 master alloy is 10%.

4. The high-strength and high-toughness Al-Si cast aluminum alloy according to claim 1, characterized in that, Zr is added in the form of an Al-Zr5 master alloy, and the mass percentage of Zr in the Al-Zr5 master alloy is 5%; Zr forms an Al3Zr dispersed phase with the Al matrix, which is used to refine the primary α-Al phase and pin dislocation movement.

5. A high-strength and high-toughness Al-Si cast aluminum alloy according to claim 1, characterized in that, Ti is added in the form of AlTi5B master alloy, and the mass percentage of Ti in AlTi5B master alloy is 5% and the mass percentage of B is 1%.

6. A method for preparing a high-strength and high-toughness Al-Si cast aluminum alloy according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Raw material preparation: Weigh out A356.2 aluminum ingot, Al-Cu50 master alloy, Al-Zn30 master alloy, magnesium ingot, AlTi5B master alloy, Al-Sr10 master alloy, Al-Zr5 master alloy and refining agent according to the alloy composition. S2: Melting treatment: The melting furnace is first heated to 520-540℃ and held for 20 minutes, then heated to 750-770℃. A356.2 aluminum ingot, Al-Cu50 master alloy, and Al-Zn30 master alloy are added. After they are completely melted, the temperature is lowered to 740℃ and magnesium ingot is added until they are completely melted. S3: Refining and modification treatment: At 740℃, AlTi5B master alloy is first added to the melting furnace and melted, then Al-Sr10 master alloy and Al-Zr5 master alloy are added until completely melted; S4: Refining process: A protective gas is introduced into the melt, and powdered refining agent is sprayed into the melt and stirred to remove gas and slag. After standing, the composition is analyzed. The refining temperature is 720-740℃, the refining time is 10-20min, the degassing temperature is 725-740℃, and the degassing time is 900-1500s. S5: Low-pressure casting: After the composition test is qualified, the holding furnace is moved to the low-pressure casting equipment; the holding temperature for low-pressure casting is 705-725℃. S6: Heat treatment: The product after low-pressure casting is subjected to solution treatment, water quenching treatment and aging treatment in sequence to obtain a high-strength and tough cast aluminum alloy.

7. The method for preparing a high-strength and high-toughness Al-Si cast aluminum alloy according to claim 6, characterized in that, The refining agent in S4 is a chloride or fluoride or a mixture of chloride and fluoride; the protective gas is at least one of nitrogen, argon and helium.

8. The method for preparing a high-strength and high-toughness Al-Si cast aluminum alloy according to claim 6, characterized in that, The forming pressure of the low-pressure casting in S5 is 200-450 mbar, the forming speed is 40-70 mm / s, and the holding time is 65-150 s; the rotor speed of the low-pressure casting equipment is 410-450 r / min.

9. The method for preparing a high-strength and high-toughness Al-Si cast aluminum alloy according to claim 6, characterized in that, In S6, the solution treatment temperature is 500-550℃ and the treatment time is 5-6h; the water temperature for water quenching is 50-80℃ and the transfer time from taking it out of the solution furnace to entering the water is <10s; the aging treatment temperature is 100-150℃ and the treatment time is 7-8h, followed by air cooling.

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